1. Field
The present disclosure generally relates to the field of iontophoresis, and in particular, to an iontophoresis device capable of preventing or suppressing an electrode reaction in an electrode assembly.
2. Description of the Related Art
JP 3030517 B, JP 2000-229128 A, JP 2000-229129 A, JP 2000-237326 A, JP 2000-237327 A, JP 2000-237328 A, JP 2000-237329 A, JP 2000-288097 A, JP 2000-288098 A, and WO 03/037425, the disclosures of which are incorporated herein by reference, disclose iontophoresis devices for administering an active agent capable of dissociating into ions (active agent ions) of positive or negative polarity.
Iontophoresis involves driving an active agent dissociated to positive or negative ions in solution by using an electrical potential to transdermally transfer the active agent into a subject, and may be advantageous such as reducing the burden placed on a subject, or improving controllability of the amount of the active agent to be administered.
FIG. 9 is an explanatory view showing the basic configuration of an iontophoresis device for performing iontophoresis.
The iontophoresis device comprises: an active electrode assembly 110 having an electrode 111 and an active agent solution reservoir 114 that holds a solution of an active agent which dissociates into positive or negative active agent ions (an active agent solution); a counter electrode assembly 120 having an electrode 121 and an electrolyte solution reservoir 122 that holds an electrolyte solution; and an electric power source 130 that includes terminals connected to the electrodes 111 and 121. An electrical potential having the same polarity as that of an active agent ion is applied to the electrode 111 and an electrical potential having a polarity opposite to that of the active agent ions is applied to the electrode 121 when the active agent solution reservoir 114 and the electrolyte solution reservoir 122 are brought into contact with the biological interface of a subject, thus delivering the active agent ions to the subject.
One issue to be investigated in such iontophoresis devices concerns various electrode reactions that may occur in the electrode assemblies 110 and 120.
For example, when an active agent is a cationic active agent that dissociates into positive active agent ions, hydrogen ions or oxygen gas may be generated at the electrode 111 and hydroxide ions or hydrogen gas may be generated at the electrode 121 due to the electrolysis of water. In addition, the active agent may cause a chemical reaction near the electrode 111 to change upon energization depending on the kind of the active agent. Furthermore, when the active agent solution reservoir 114 contains chlorine ions, this may cause chlorine gas or hypochlorous acid to be generated.
Similarly, when an active agent is an anionic active agent that dissociates into negative active agent ions, hydroxide ions or hydrogen gas may be generated at the electrode 111 and hydrogen ions or oxygen gas may be generated at the electrode 121 due to the electrolysis of water. In addition, the active agent may cause a chemical reaction near the electrode 111 to change upon energization depending on the kind of the active agent. Furthermore, when the electrolyte solution reservoir 122 contains chlorine ions, this may cause chlorine gas or hypochlorous acid to be generated.
If a gas is generated in the electrode assembly 110 or 120 as described above, energization from the electrode 111 or 121 to the active agent solution or the electrolyte solution may be inhibited. When hydrogen ions, hydroxide ions, or hypochlorous acid are generated in the electrode assembly 110 or 120, the ions and/or acid may be transferred to a biological interface. In addition, the alteration of an active agent may cause conditions such as the inability to obtain an initial active agent effect, and/or the production of toxic substances.
U.S. Pat. No. 4,744,787 discloses an iontophoresis device capable of addressing problems such as those described above. A silver electrode is used as an anode and a silver chloride electrode is used as a cathode.
An electrode reaction may preferentially occur in this iontophoresis device, where silver in the anode is oxidized to become insoluble silver chloride, while silver chloride is reduced at the cathode to become metallic silver. The generation of various gases and the production of various ions due to such electrode reactions as described above may thus be suppressed as a result.
However, it may be difficult to prevent dissolution of the silver electrode during storage of the iontophoresis device. In particular, the number of kinds of applicable active agents may be limited when the device is intended for administering a cationic active agent. In addition, the morphological change upon production of silver chloride from the silver electrode is large. Therefore, special consideration must be given in order to prevent morphological changes from affecting the properties of the device. As a result, certain restrictions may be imposed on the shape of the device (for example, it may not be possible to employ a laminate structure.) Furthermore, an active agent may be altered upon energization.
JP 3,040,517 B discloses an iontophoresis device shown in FIG. 10.
The iontophoresis device comprises an active electrode assembly 210 including an electrode 211, an electrolyte solution reservoir 212 that holds an electrolyte solution in contact with the electrode 211, an ion exchange membrane 213 of a second polarity, the ion exchange membrane 213 placed on the outer surface side of the electrolyte solution reservoir 212, an active agent solution reservoir 214 that holds an active agent solution containing an active agent ion of a first polarity, the active agent solution reservoir 214 placed on the outer surface side of the ion exchange membrane 213, and an ion exchange membrane 215 of the first polarity, the ion exchange membrane 215 placed on the outer surface side of the active agent solution reservoir 214; and a counter electrode assembly 220 and an electrode 230 similar to those shown in FIG. 9.
The electrolyte solution and the active agent solution are partitioned by the second ion exchange membrane 213 of the second polarity. As a result, the composition of the electrolyte solution can be selected independently of the active agent solution. An electrolyte solution that does not contain chlorine ions may be used, and an electrolyte having a lower oxidation or reduction potential than the electrolysis of water may be selected as the electrolyte in the electrolyte solution to suppress the production of oxygen gas, hydrogen gas, hydrogen ions, or hydroxide ions resulting from the electrolysis of water. Alternatively, the use of a buffer electrolyte solution into which a plurality of electrolytes are dissolved may suppress changes in pH due to the production of hydrogen ions or hydroxide ions. Furthermore, the transfer of an active agent ion to the electrolyte solution reservoir may be blocked by the second ion exchange membrane, helping to prevent changes in the active agent due to chemical reactions occurring upon energization.
The iontophoresis device disclosed in JP 3,040,517 has a large number of constitutive elements, and the electrolyte solution reservoir 212 and the active agent solution reservoir 214 must be handled in a wet state (a state where there is a high water content). A problem may thus arise in that automated production and/or mass production of the device may be difficult to achieve. In addition, production costs may not be reduced significantly.